1. Field of the Invention
This invention pertains to a lighting fixture and more particularly to an improvement in providing improved spill light characteristics to a lighting fixture with an elongated parabolic or similarly advantageously constructed reflector.
2. Description of the Prior Art
Light fixture housings and their light reflector systems used in conjunction with high intensity, gaseous discharge (HID) lamps are generally relatively complex structures. Reflectors used in such structures are preferably curvilinear so as to parabolically or otherwise advantageously reflect light from the fixture. Also, necessarily, such reflectors must accommodate to the elongated lamp structures which are used in the industry for HID lamps. Most HID lamps are elongated. Many fixtures include reflectors having multiple curved segments or segments which are complexedly curved with respect to one or more axes or focal points.
An example of a common type of reflector system is shown in patent application Ser. No. 21,269, now Pat. No. 4,261,030, entitled "Wraparound Parabolic Light Fixture and Method for Manufacture" filed Mar. 15, 1979, of the same inventor as the present application and commonly assigned, which application is incorporated herein by reference for all purposes. That reflector type is sometimes referred to as a trough reflector due to its appearance.
As explained in the above-identified patent application, there is an advantage to shaping the principal reflector to be in a parabolic shape because the emanating light from such a reflector is reflected in parallel fashion. It is often a requirement that such a light be used when wide area spill light from the fixture should be minimal. Spill light is a measure of focal efficiency of the overall reflector. Generally, spill light is that 10 percent of the light which is not within the 90 percent of the light emanating in the most focused direction. Light from such a fixture brightly illuminates the area directly in front of the fixture, or in other words, along the lines parallel to the principal reflection aiming axis.
Light also emanates from the ends of the lamp bulb, however, and without a reflecting surface would not result in additional light being reflected from the fixture. Therefore, to make the light fixture more efficient than otherwise, planar end reflectors are provided. Such reflectors are not made parabolic, however, primarily because it is expensive to make them of such shape for the incremental benefit that such a shape would make. These planar end reflectors reflect light in directions other than straightforward. These emanations do not just reflect outwardly from the ends of the lamp but also cross reflect and reflect at angles sideways to the fixture so that they, in part, do defeat the parabolic radiations from the principal reflector and result in wide area spill light.
Louvers and other light restrictions can be employed, but only at the expense of sharply decreasing light efficiency. This is also true of darkening selected reflecting surfaces compared with the specular treatment of other surfaces.
Therefore, it is a feature of the present invention to provide an improved trough-type parabolic light fixture in which the light reflections emanating from the end reflectors do not radiate at an appreciable angle to the straightforward direction.
It is another feature of the present invention to provide an improved light fixture having a cutoff element which does not appreciably interfere with its straightforward reflections, while largely preventing spurious sideways or spill light reflections.